1. Field of the Invention
This application relates to the field of vibration analysis and more particularly to the field of performing vibration analysis for the purpose of providing device adjustments that reduce vibrations.
2. Description of Related Art
Rotors which propel helicopters and other propeller-driven aircraft induce vibrations in the structure supporting the rotor. The vibrations occur at frequencies that correspond to the shaft rotation rate and harmonics thereof. The vibrations may result in a structural damage, crew fatigue, and ultimately become one of the factors limiting the maximum forward speed of the aircraft. Similar types of vibrations are produced by fans and compressors and fixed installations as well as by marine propellers.
A primary source of the vibration problem is non-uniform air loads on the blades, although mass imbalance is not uncommon. Aerodynamic anomalies, however, tend to develop recurrently due to blade wear, damage, deformation, etc. The aerodynamic and mass and stiffness distribution anomalies have often been called “tracking faults”, since a primary observable feature of the uneven air loads or mass distribution is it tendency for the blades to flap and/or deflect unevenly, and thus follow different “tracks”. The troublesome manifestation of the aerodynamic and mass imbalance, however, is usually the 1/rev and n/rev vibrations and not the track deviations themselves.
It is possible to modify the vibration characteristics of a helicopter by “rotor trimming”, which involves adjusting the weight of the blades at the hub (weights), the tab setting(s) at one or more blades (tabs), and the adjustment on the pitch rods (pitch control rods or PCRs). However, determining the effect of each of these adjustments may be difficult because the interdependence of the adjustments. This interdependence may be the source of some difficulty with trial and error methods of rotor trimming, which may allow variation of only one type of adjustment at a time. One set of adjustments may be thrown out of kilter by a subsequent step in the process, requiring repetitive adjustments which may or may not converge to an acceptable state. Some helicopter rotor trim balancing methods rely, at least in part, upon making the track of each blade identical using, for example, known optical methods.
Mechanical balancing of rotors with mass imbalance may, in some cases, be performed with a single accelerometer and a shaft-phase reference sensor. However, uneven air loads may not be fully diagnosed and corrected with such a technique. Other techniques used to perform the rotor smoothing function may rely upon optical tracking in conjunction accelerometers. Known rotor smoothing systems, however, process vibration data in such a way that there may be an inherent ambiguity in the interpretation of the signatures. The ambiguity comes about because, in many cases, the number of channels processed simultaneously is inadequate to fully separate translational and rotational acceleration components at a given point. Thus, the motion of the helicopter (and in particular the rotor support) in response to a rotor anomalies may be incompletely specified. Furthermore, some systems may not deduce the corrections needed from the Fourier coefficients related to each anomaly.
Existing techniques for rotor smoothing may utilize a variety of different options, and combinations thereof, in connection with determining what adjustments to make to reduce vibration. An operator may have to provide a selection of one or more options as inputs to such a technique. For example, an operator using a technique for determining a set of adjustments for reducing vibration may be required to provide inputs selecting which one or more types of sensor data to use (e.g., vibration alone, vibration and tracking, tracking alone), selecting one or more optimization goals or solution strategies, and the like. Providing such inputs may be cumbersome and intimidating for an inexperienced user. Furthermore, an inexperienced user may select a set of inputs which may not be desirable given a current set of sensor data characterizing vibration in an existing system or arrangement. Similarly, a set of default inputs may not be desirable for the current set of sensor data characterizing the vibration in an existing system.